Category : Tutorials + Patches
Archive   : TXTFILES.ZIP
Filename : ROMDATA.TXT

The ID comes from the second to last byte in the IBM ROM
which is used by IBM to encode the type of machine. The value of
the byte at location FFFFE (hexadecimal) directly corresponds to
the machine type as is shown by this table:

Sub
ID Model
Byte Byte Machine Date Revision
------------------------------------------------------------
FF 00 = PC All -
FE 00 = PC-XT 11/08/82 -
FD 00 = PCjr ? -
FC 00 = PC-AT 1/10/84 -
FC 00 = PC-AT 6/10/85 Rev. 1
FC 01 = PC-AT 11/15/85 Rev. 0
FC 02 = PC-XT286 4/21/86 Rev. 0
FC 04 = PS/2 Model 50 2/13/87 Rev. 0
FC 05 = PS/2 Model 60 2/13/87 Rev. 0
FB 00 = PC-XT 1/10/86 Rev. 1
FB 00 = PC-XT 5/09/86 Rev. 2
FA 00 = PS/2 Model 30 9/02/86 Rev. 0
F9 00 = PC-Convertible 9/13/85 ?
F8 00 = PS/2 Model 80 ? ?


Checking the BIOS date is the most useful method to
determine the version of ROM which is present in your machine.
In accumulating data over the years I have seen or heard of these
dates reported:

Type Date Comments
-----------------------------------------------------------------
PC 04/24/81 Found in very early PC's only, Rarely seen.
Has several bugs fixed in later versions.
This ROM does not support more that 576k of
RAM, or Hard Disk. Upgrade is recommended.
-----------------------------------------------------------------
PC 10/19/81 Indicates early PC with 64k motherboard. This
ROM does not support more that 576k of RAM,
booting from a Hard Disk, Enhanced Graphics
Adapter, or any ROM on adapters. Upgrade is
recommended.
-----------------------------------------------------------------
PC 10/27/82 Indicates later PC-2 with 256k motherboard.
This ROM supports 640k and Hard Disk boot.
Has ROMSCAN feature to allow ROM expansion on
adapter cards. Available from IBM as an
upgrade to all PC's.

ROM ID indicates Machine Type is: PC -- ID is FF
ROM BIOS Date is................: 10/27/82
ROM Part Number is..............: 1501476
-----------------------------------------------------------------
PCC 09/13/85 Indicates PC Convertible laptop. Compatible
with the later PC and XT ROMs, although
internally it is significantly different. Has
support for new 3.5" Diskette Drives.

ROM ID indicates Machine Type is: PC Convertible -- ID is F9
ROM BIOS Date is................: 09/13/85
ROM Part Number is..............: 7396918
-----------------------------------------------------------------
XT 08/16/82 Indicates an XT with Type 1 Motherboard. Seen
only in very early XT's. Actually contains ID
byte which improperly indicates PC. Little is
known otherwise. Very rare.
-----------------------------------------------------------------
XT 11/08/82 Indicates an XT or Portable PC with a Type 1
Motherboard. This is the most common ROM
found in these machines.

ROM ID indicates Machine Type is: XT -- ID is FE
ROM BIOS Date is................: 11/08/82
ROM Part Number is..............: 1501512
-----------------------------------------------------------------
XT 01/10/86 Indicates a new XT. This machine comes with
half height floppies, optional 20m hard disk
and up to 640k on the Motherboard. Has
support for 1.2m and 3.5" 720k Drives. Has
new 3270 style keyboard (101 keys) as a
standard item. BIOS shows extensive changes,
is now a total of 64k in size. Appears much
like the current AT ROM.

ROM ID indicates Machine Type is: XT (Type 2) -- ID is FB
ROM BIOS Date is................: 01/10/86
ROM Part Number is..............: 62X0851
-----------------------------------------------------------------
XT 05/09/86 Indicates fixed version of previous ROM.
Fixes a problem with certain IBM PC-NETWORK
adapters. This is the current ROM, and is
available only with a complete motherboard
swap.

ROM ID indicates Machine Type is: XT (Type 2) -- ID is FB
ROM BIOS Date is................: 05/09/86
ROM Part Number is..............: 62X0890
-----------------------------------------------------------------
AT 01/10/84 Indicates the original version AT with 128k
piggy backed RAM chips and large (Type 1)
motherboard. Support for 14 Fixed Disk types.
POST not timing sensitive, will not detect
clock rate increase through altered crystal
frequency.

ROM ID indicates Machine Type is: AT -- ID is FC
ROM BIOS Date is................: 01/10/84
ROM Part Number is..............: 6181028
-----------------------------------------------------------------
AT 06/10/85 Indicates new AT version using 512k chips and
reduced size (Type 2) motherboard. Support
for 22 Fixed Disk types including IBM 30m
Fixed Disk. Has support for 3.5" 720k Drives.
This ROM supplied with IBM 30m Fixed Disk
upgrade option for older models. Improved
POST checks many timing dependent functions,
will fail if clock rate is greater than 6Mhz.

ROM ID indicates Machine Type is: AT -- ID is FC
ROM BIOS Date is................: 06/10/85
ROM Part Number is..............: 6480090
-----------------------------------------------------------------
AT 11/15/85 Indicates new AT version running 8 Mhz system
clock. Standard configuration includes 30m
Fixed Disk, 512k, Serial/Parallel Adapter,
and the new 3270 style keyboard (101 keys).
System features 512k chips and reduced size
(Type 2) motherboard. Support for 23 Fixed
Disk types. Has support for 3.5" Drives in
720k and 1.44m capacities. POST altered for
faster clock, fails if clock rate is greater
than 8Mhz.

ROM ID indicates Machine Type is: AT -- ID is FC
ROM BIOS Date is................: 11/15/85
ROM Part Number is..............: 61X9266
-----------------------------------------------------------------
AT 04/21/86 Indicates an XT-286. The ID byte of this
machine indicates an AT. This is an AT in
every way except the physical exterior. Has
updated rom with support for 24 Fixed Disk
types. Has support for 3.5" Drives in 720k
and 1.44m capacities. Runs 6Mhz with 0 wait
states. Motherboard physical dimensions
almost same as XT. (8.5 x 13.2)

ROM ID indicates Machine Type is: AT -- ID is FC
ROM BIOS Date is................: 04/21/86
ROM Part Number is..............: 78X7462
-----------------------------------------------------------------

The ROM Part Number could be potentially useful for
specifying an upgrade or repair chip if needed. Unfortunately,
IBM does not readily sell these ROMs, and when they do, the
transaction requires either that you supply the old ROM in
advance, or that you have the upgrade performed by an authorized
dealer. ROM chips are available as an upgrade (exchange) only
and are not available as a repair or service item, for repair
work IBM will only sell you an entire motherboard! Currently
only the PC ROM dated 10/27/82 is available for the PC as a
separate part, and the AT ROM dated 06/10/85 is available only
with the IBM 30m Fixed Disk. It is not currently found as a
separate part. The fix ROM for the Type 2 Motherboard XT is only
available with a complete motherboard swap, which is free if you
call IBM and tell them that you have a problem with certain PC-
NETWORK adapter cards. All of the other ROMs, including any for
the XT, are simply not available. You cannot use a ROM from a

different machine type, such as an AT ROM in a PC.

For those interested in the IBM PC ROM upgrade, the IBM Part
Number for the PC BIOS Update Kit is: 1501005. This is not the
actual part number in the chip, this is instead the number for
the upgrade kit which your dealer can obtain.

Any questions may be addressed to Scott Mueller at:

Mueller Business Systems
227 S. Hale
Palatine, IL 60067
(312) 358-5524

I would especially like to hear from anyone who can add to the
information contained here, such as ROMs with dates or part
numbers not listed.